The color value specifies the color of the shadow. The
horizontal offset is a length value that specifies the distance to the
left or right of the text that the shadow has to be rendered. A positive value
renders the shadow text to the right, a negative value renders it to the left.
The vertical offset is a length value that specifies the vertical distance from
the text that the shadow has to be rendered. The blur radius, a
length value, controls
the blurriness of the shadow.

More than one shadow can be specified — each set of values are
separated by a comma.

In the above example, the text has two shadows — one below and the
other above. Firefox 3 and Internet Explorer 8 and below ignore the
text-shadow property. Firefox 3.5, Safari 4, Chrome 3 and Opera 10
display the text shadows as shown in the picture.

Conclusion

Since the text-shadow property is ignored by Firefox 3 and
Internet Explorer 8 and below, this property cannot be used.